The present invention relates to internal combustion engines and pertains particularly to an improved delay stroke piston assembly for reciprocating piston engines.
The reciprocating piston internal combustion engine is the primary source of power for most automotive vehicles throughout the World today. The internal combustion engine has gained widespread use because of its many advantageous attributes which are well known. However, one of its main drawbacks, namely that of environmental pollution, raises the need for improvements in the combustion efficiency thereof.
The reciprocating piston internal combustion engine is manufactured in either two-stroke or four-stroke versions. The four-stroke engine is most widely used in the automobile. However, recent emphasis on economy and fuel efficiency has focused attention on the two stroke engine because of its higher horsepower to weight advantage. The two-stroke engine achieves this advantage because of its higher number of power strokes for a given revolution per minute (rpm). This advantage is largely outweighed by other disadvantages, primarily in the area of combustion and/or scavenging efficiency.
Federal regulations are imposing increasingly stricter standards for fuel efficiency and exhaust emissions on the automobile industry. Many ancillary systems have evolved for controlling pollutants by controlling spark and injection timing as well as exhaust gasses. The systems for controlling exhaust gasses typically increase cost and reduce the efficiency of the engine.
The piston in the four-stroke engine makes four strokes in the cylinder for each power stroke. The piston begins at top dead center (TDC) moving downward with an intake valve open to create a partial vacuum for drawing in a combustion charge. At the end of this stroke, the piston begins a compression stroke with all valves closed compressing the charge as the piston reaches top dead center. The fuel in the compressed charge is ignited as the piston reaches generally top dead center, and the rapidly burning (exploding) charge drives the piston down on the power stroke applying torque to the crankshaft. When the piston reaches bottom dead center (BDC), it begins an exhaust stroke as the exhaust valve opens, and drives the combustion waste from the cylinder as it moves to the top on the exhaust stroke.
Due to inefficiencies in the valves, pistons and associated combustion and scavenging dynamics, an absolute fresh intake charge is difficult to draw in. Similarly, for the same reason, a complete exhaust of the spent charge is difficult to achieve.
There exists a need for a two-stroke internal combustion engine having means for improving the intake and exhaust efficiency.